In the United States, urogenital infections with Chlamydia trachomatis are the leading sexually transmitted disease with an estimated 10 million new cases reported each year. The urogenital infections result in involuntary infertility in 100-200,000 women each year. It is estimated that equal or greater numbers of these infections occur in European countries. In addition, ocular infection with C. trachomatis results in blinding trachoma which afflicts approximately 500 million individuals from developing countries. Improved diagnostic methodologies and vaccines or immunoprophylactic preventative measures are needed to manage and control the disease.
Chlamydia trachomatis isolates occur as 15 distinct serovars. Based on serological relatedness, these 15 serovars have been divided into three serogroups; B serogroup (serovars B, Ba, D, E, L1 and L2), intermediate serogroup (serovars F, G, K and L3), and C serogroup (serovars A, C, H, I and J). The antigen that confers serovar and serogroup-specificities to chlamydia is the major outer membrane protein (MOMP), and protective immunity developed during chlamydial ocular infection is thought to be directed at serovar and serogroup MOMP determinants.
The genes encoding the MOMP of the C. trachomatis serovars A, B, C, L1 and L2 have been cloned and sequenced (Pickett et al., FEMS Microbiol. Lett. 42:185-190 (1987); Stephen et al., J. Bacteriol. 168:1277-1282 (1986); and Stephens et al., J. Bacteriol 169:3879-3885 (1987); Baehr et al., Proc. Natl. Acad. Sci. USA, 85:4000-4004 (1988)). Comparative analysis of their amino acid sequences show the MOMP genes to be highly conserved structures that contain four evenly spaced domains whose sequences vary among the different serovars. The locations of these nucleotide and amino acid sequence variable domains (VDs) are:
VDI--nucleotides 256-315 and residues 64-83; PA1 VDII--nucleotides 481-546 and residues 139-160; PA1 VDIII--nucleotides 736-777 and residues 224-237; PA1 VDIV-nucleotides 928-1017 and residues 288-317. PA1 Group 1--serovars B, Ba, D, E, L1 and L2; PA1 Group 2--serovars G and F; PA1 Group 3--serovars A, C, H, I, J, K and L3.
Epitope mapping has shown that three of the four VD domains (I, II and IV) contain contiguous antigenic determinants which elicit the formation of serovar, subspecies (determinants common to three or more serovars within a serogroup), serogroup or species-specific antibodies.
Variable domains I and II, which demonstrate the greatest amount of inter serogroup sequence variation, are the locations of the serovar-specific determinants. Variable domain IV is the largest of the MOMP VDs and is located near the C-terminus of the protein. VDIV is the location of subspecies and serogroup antigenic determinants, as well as a highly conserved species-specific antigenic determinant. Antigenic determinants have not been mapped to VDIII, the smallest and least variable domain of the MOMP genes.
Variable domains I, II and IV of the MOMP of C. trachomatis protrude from the cell surface towards the external environment as demonstrated by their susceptibility to cleavage by trypsin, and their accessibility to antibody binding. Trypsin cleavage in both VDII and VDIV, but not within VDIV alone, decreases chlamydial attachment to HeLa cells suggesting that these domains, or conformational MOMP structures that are dependent on the integrity of these domains, may function as a chlamydial ligand.
Based on the immunological and biological relationships among MOMP VD structure and function, and the fact that the MOMP VDs appear to be the major variable sequences between serovars, the present inventors sought to identify the nucleotide and amino acid sequences of the MOMP VDs I-IV of C. trachomatis serovars Ba, D, E, F, G, H, I, J, K and L3, and to confirm those of serovars B, A, C, L1 and L2.